CHAPTER XII 



THE CEREBRUM AND THE LIFE OF THE 

 INDIVIDUAL 



IN some of the tissues of the body there is a constant 

 formation of new cells at every period of life. This is true 

 of the skin, and is nowhere more evident than in the case 

 of its outgrowths, the nails and the hair. In other tissues 

 there is no addition to the original number of the cellular 

 units. It has been stated in another connection (Chapter 

 VIII) that no multiplication of the units occurs in the 

 skeletal muscles, though there may be an increase in the 

 diameter of the fibers. It is a most significant fact that 

 in the nervous system the maximum number of the 

 neurons appears to be attained very early, and hence any 

 later change will mean a diminution. The great ad- 

 vances made from infancy onward to maturity are not 

 based upon any corresponding multiplication of the 

 neurons. They are accomplished in spite of a stationary 

 or even decreasing number of these elements, and must be 

 referred to the formation of new routes of communication 

 among them. 



It has been said that the limited powers of the nervous 

 system in the newborn are indicative of the great individual 

 development which awaits realization. This subject may 

 now be pursued in some detail. The receptor system of the 

 infant is probably complete. On the effector side the 

 muscles, especially those of the legs, have yet to grow 

 considerably to sustain a proper proportion to the total 

 mass of the body, but they are fully provided with efferent 

 fibers from the motor cells of the lower order in the cord 

 and brain. The department of the nervous system which 

 is farthest from its future condition is the intermediate 



153 



